Fecal Microbiota Transplantation for Gastrointestinal Complications After Allogeneic Hematopoietic Cell Transplantation: A Systematic Review and Narrative Synthesis

Following allogeneic hematopoietic stem cell transplantation (allo-HSCT), patients frequently develop gastrointestinal complications, including microbiota dysbiosis, infectious syndromes, and graft-versus-host disease (GVHD), which remain major contributors to post-transplant morbidity and mortality. In recent years, several studies have explored microbiome-based interventions, particularly fecal microbiota transplantation (FMT), as a therapeutic strategy for these complications in this highly immunocompromised population. However, substantial variability exists across studies with respect to clinical indications, FMT protocols, and reported outcomes. To systematically evaluate the reported clinical use of FMT for gastrointestinal complications following allo-HSCT, including microbiota dysbiosis, infectious complications, and GVHD. The aim was to characterize study populations, treatment protocols, and reported clinical outcomes, and to synthesize evidence regarding efficacy and safety, with a focus on indication-specific patterns and potential translational relevance for patient management in this highly immunocompromised population. We conducted a PRISMA-compliant systematic review of studies evaluating FMT as a treatment in patients after allo-HSCT. PubMed, Embase, Web of Science, and the Cochrane Library were searched through October 2025. Eligible studies included randomized controlled trials, cohort studies, and prospective or retrospective single-arm studies reporting clinical outcomes following FMT. Given the marked heterogeneity in clinical indications, FMT administration strategies, and outcome definitions, study findings were synthesized using a structured narrative approach, with quantitative data summarized descriptively where appropriate. Twenty studies including patients after allo-HSCT were analyzed. FMT demonstrated high and consistent response rates in non-GVHD indications, whereas GVHD cohorts exhibited more variable responses, with median CR and ORR ranging 50% to 55% in steroid-refractory cases. One-year overall survival was generally favorable in dysbiosis and infection groups (>70%), but more heterogeneous in GVHD. FMT was well tolerated, with predominantly mild gastrointestinal adverse events; serious events were infrequent and mostly disease-related. Current evidence indicates that FMT has been explored as a context-dependent therapy for selected gastrointestinal complications following allo-HSCT, particularly in patients with acute GVHD. Nevertheless, substantial heterogeneity in study design, clinical indications, and outcome assessment limits definitive conclusions regarding efficacy. Well-designed prospective studies with standardized treatment indications, outcome measures, and careful consideration of concurrent immunosuppressive therapies are required to better define the optimal role, timing, and patient selection for FMT in the post-transplant treatment setting.